Field of the Disclosure
The present disclosure relates to an organic light emitting diode (OLED) display device, and more particularly, to an organic light emitting diode display device capable of reducing the number of lines between a timing controller and a data driving IC.
Discussion of the Background
Flat panel displays that display images using digital data are typically liquid crystal displays (LCDs) using liquid crystals and OLED display devices using organic light emitting diodes (OLEDs).
Of these, OLED display devices are self-luminous devices that emit organic light-emitting layers by recombination of electrons and holes, and are expected to be the next generation display devices because of their high brightness, low driving voltage and thinness.
FIG. 1 is a configuration diagram of an OLED display device according to the related art.
As shown in FIG. 1, the related art OLED display device includes display panel 1 having a plurality of pixels arranged in a matrix form and defined in a region where a plurality of gate lines GL and data lines DL intersect, a timing controller 4 for aligning video signals inputted from the outside and controlling the operation timing of each pixel, and a gate driver 3 and a data driver 2 for driving gate lines GL and data lines DL provided in the display panel 1 in accordance with signals outputted from the timing controller 4.
Here, the gate driver 3 includes a plurality of gate driving ICs, and the data driver 2 also includes a plurality of data driving ICs.
Each pixel of the display panel 1 includes an OLED element composed of an organic light emitting layer between an anode and a cathode, and a pixel circuit for independently driving the OLED element.
The pixel circuit includes a switching thin film transistor (TFT) TR1 for supplying a data voltage to a storage capacitor Cst according to a scan signal, a driving TFT TR2 for supplying a driving current to the OLED element according to a driving voltage charged in the storage capacitor Cst, and a sensing TFT TR3 for sensing a threshold voltage variation and a mobility variation of the driving TFT. Therefore, the OLED element generates light proportional to a driving current.
In the OLED display device, there is a problem that the driving characteristics (i.e., threshold voltage, mobility, and etc.) of the driving TFT are varied due to a process variation and a change with the passage of time, thereby causing non-uniform luminance. In order to solve this problem, an OLED display uses a compensation method of sensing driving characteristics of each pixel and compensating data to be supplied to each pixel by using the sensed driving characteristics.
In the related art image quality compensation technique, the method and period for sensing the threshold voltage change amount of the driving TFT and the mobility variation amount of the driving TFT are different from each other.
FIG. 2 is a diagram for explaining the related art image quality compensation technique, and FIG. 3A is a graph of a pixel circuit configuration and a time and voltage relationship for explaining a sensing principle for extracting a threshold voltage change of a drive TFT in the related art image quality compensation technique, FIG. 3B is a graph of a pixel circuit configuration and a time and voltage relationship for explaining a sensing principle for extracting a mobility change of a driving TFT in the related art image quality compensation technique.
As shown in FIGS. 2 and 3A, the sensing method for extracting the change in the threshold voltage Vth of the driving TFT is performed by receiving a source voltage Vs of the driving TFT as a sensing voltage VsenA after operating the driving TFT in a source follower manner and then detecting a threshold voltage change amount of the driving TFT based on the sensing voltage VsenA. The threshold voltage change amount of the driving TFT is determined according to the magnitude of the sensing voltage VsenA, thereby obtaining an offset value for data compensation. In this sensing method, since the sensing operation must be performed after the gate-source voltage Vgs of the driving TFT operated in the source follower mode reaches the saturation state, the sensing time is long and the sensing speed is low. This sensing method is referred to as a slow mode sensing method.
As shown in FIGS. 2 and 3B, the sensing method for extracting the change in the mobility μ of the driving TFT is performed by turning on the driving TFT by applying a constant voltage Vdata+X higher than the threshold voltage, in order to define the current capability characteristics excluding the threshold voltage (Vth) of the driving TFT, and receiving the source voltage Vs of the driving TFTs charged for a predetermined time as a sensing voltage VsenB, where X is a voltage in accordance with the offset value compensation. The mobility change amount of the driving TFT is determined according to the magnitude of the sensing voltage VsenB, thereby obtaining a gain value for data compensation. This sensing method is characterized in that the time required for sensing is short and the sensing speed is fast since this sensing method is performed in a state in which the driving TFT is turned on. This sensing method is referred to as a fast mode sensing method.
Since the sensing speed of the slow mode sensing method is slow, a sufficient sensing period is required. That is, the slow mode sensing method for sensing the threshold voltage of the driving TFT must be performed until the driving power is turned off after the image display is completed, in response to the power off command signal from the user, so that the sensing time can be sufficiently allocated without being recognized by the user.
On the other hand, the fast mode sensing method for sensing the mobility of a driving TFT has a high sensing speed. Therefore, the fast mode sensing method may be performed in the vertical blank periods within the display driving period, before the image display is performed after the driving power is turned on in response to the power-on command signal from the user.
In order to sense the driving characteristics of each pixel and to compensate data to be supplied to each pixel using a sensing value, video signal transmission lines for transmitting video signal from the timing controller 4 to the data driver 3 and a separate line B-LVDS for transmitting the sensing value to the timing controller 4 exists between the timing controller 4 and the data driver 3.
FIG. 4 is a block diagram showing the configuration of the related art timing controller 4 and the data drivers 3(3a, 3b and 3c).
The timing controller 4 transmits the video signal to each data driving IC 3a, 3b, and 3c. Of the data driver 3 through an EPI (Embedded Point-to-Point Interface) interface known as a high-speed serial interface. The data driver 3 transmits the sensing value to the timing controller 4 through a separate low voltage differential signal (LVDS) interface. Therefore, the OLED display device requires a separate LVDS interface in addition to the EPI interface in order to transmit the sensing value. Accordingly, the OLED display device has a size of the control PCB larger than that of the liquid crystal display device, and the number of pins of the timing controller of the OLED display device is increased.